Consumer awareness of product freshness has led to the widespread practice of addressing this issue by means of appropriate product labeling. Where relevant, the label will typically provide information related to the freshness and suggested storage method of the product. This information may include a date of manufacture, a “sell by” date, or a “best before” date. A “sell by” date specifies by which date the product should have been sold to the consumer. A “best before” date specifies by when the product should be disposed of by vendor or consumer.
The recommended storage method typically specifies whether the product is to be stored in the refrigerator or freezer and whether this storage method is to be used from the time of purchase or from the time of first opening. The former method is typically used for dairy products, whereas the latter method is usually more appropriate for jams, sauces conserves and liquid medications. For some items the labeling will also specify for how long the product may be kept after it has first been opened. The reasoning behind this is that if the product is produced and packed under conditions that eliminate deterioration, such deterioration will only occur following this first opening. Alternatively, product deterioration may commence at manufacture, but be dramatically accelerated once it is exposed to air. In either case, it is important to monitor the time since opening and not just the marked shelf-life.
A number of products have been developed and commercialized that implement the concept of active labeling. These products contain a chemical system or liquid migration system which provides a color change over time, either as a function of elapsed time since activation, or by integrating time and temperature since activation. The latter are termed TTIs (time-temperature indicators) whereas the former primarily indicate the passage of time. Herein both types of indicator are referred to generically as “lifetime indicators” or simply “indicators”. The specifications of a TTI can be set to emulate those of the foodstuff in the package. Thus, given that the TTI placed on the package and activated as the food is produced, the TTI gives an accurate indication of the food freshness which takes into account the vagaries of the distribution chain. In particular, if the product has not been maintained at the appropriate temperature through a part of the distribution chain, the TTI may give the consumer an indication thereof.
U.S. Pat. Nos. 4,292,916, 5,053,339 5,446,705 and 5,633,835 describe color changing devices for monitoring the shelf-life of perishable products. These devices are initiated by physically bringing into contact reactive layers so that the reaction will start, and this action can only conveniently be performed at the time of packaging. This approach is suitable for monitoring the degradation of foodstuffs which lose freshness throughout the entire distribution chain. U.S. Pat. No. 5,555,223 describes a process for attaching timing indicators to packaging, including the step of setting the timer clock at the exact time of production.
There is a substantial proportion of food and drug stuffs, and other perishables for which significant degradation starts to occur only when the package is opened. U.S. Pat. No. 6,373,786, by the present author, hereby incorporated by reference, addresses this issue for rigid containers incorporating a rigid cap or closure. Said patent describes the integration of a lifetime indicator into the cap or closure, such that the first opening of the cap activates the lifetime indicator. In this manner, the thus incorporated lifetime indicator will show the elapsed time or time-temperature integral since the container was first opened. However, while said patent provides a good solution for rigid containers such as bottles and cartons which have a closure, many types of food, drugs and other perishables are packaged in at least partially flexible packaging such as plastic bags or shrink seal packages, and for these packages attaching the existing timers and TTIs is likely to produce misleading results in that they have no simple and foolproof means of activation at the time of opening the package.
It is therefore the intention of the present invention to obviate the shortcomings of the above-mentioned solutions by providing a simple and appropriate means of activating a lifetime indicator on first opening of an at least partially flexible package for foodstuffs medicines and other perishables, which have long shelf lives but deteriorate after opening. Thus, in the present invention, a key element is the use of an opening method which activates the lifetime indicator.